A series of complexes of Cr (III) and other metal ions with amino acids and peptides will be investigated using sharp line luminescence (SLL) spectroscopy, and utilizing the vibrational and electronic data obtained to probe the details of the metal coordination site. These systems we propose to study are intended to provide a data base to make possible extension to more complicated binding sites in metalloproteins, for which SLL offers the unique possibility of extracting site-specific vibrational data. SLL spectral data, including vibrational frequencies, intensities, combination band patterns, and electronic splittings, yield information on the ligands to which the metal ion is coordinated, the arrangement of these ligands about the metal, and, to some extent, the deviations from orthoaxiality. It thus seems likely that development of the SLL technique will have far-reaching consequences in the study of metal interactions in biological systems.